<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #outer{
            /* border: 1px solid #999; */
            width: 1000px;
            height: 950px;
            /* 技巧 - div居中显示
            当一个容器一旦设置了margin:auto之后,就不能再去设置margin-left等 */
            margin: auto;
        }
        .top{
            border: 1px solid #999;
            height: 120px;
            width: 998px;
        }
        
        .middle{
            /* border: 1px solid #999; */
            height: 700px;
            width: 1000px;
            margin-top: 2px;
        }
        .middle_left{
            border: 1px solid #999;
            width: 300px;
            height: 698px;
            float: left;
        }

        .middle_right{
            border: 1px solid #999;
            height: 698px;
            /* width: 500px; */
            float: left;
            margin-left: 2px;

            /* 重点计算width */
            /* width = 998 - 300 - 2(border) - 2(margin-left) - 2 =  */
            width: 694px;
        }

        .foot{
            border: 1px solid #999;
            margin-top: 2px;
            width: 100%;
            height: 120px;
        }
        
    </style>
</head>
<body>
    <div id="outer">
        <div class="top">

        </div>
        <div class="middle">
            <div class="middle_left"></div>
            <div class="middle_right"></div>
        </div>
        <div class="foot">

        </div>
    </div>
</body>
</html>